fix(createCollection): Db.createCollection should pass readConcern to new collection

[rosemaryy]

Fixes Node-1790

Description

Adhere to the spec by having the db.createCollection create a collection with the same readConcern of db if the readConcern isn't otherwise specified.

What changed?
In Db.createCollection, inherit the readConcern of the database db if none are specified.

[rosemaryy]

Failing the below test because the tests doesn't expect for db.createCollection to always create a new field for ReadConcern. Not sure if I should change the test to always expect a readConcern or if I should modify the code so that the new collection doesn't inherit db's readConcern value if db's readConcern value is empty.

expected
{ create: 'test', viewOn: 'users', pipeline: [ { '$match': {} } ], readConcern: {} }
to deeply equal
{ create: 'test', viewOn: 'users', pipeline: [ { '$match': {} } ] }

[kvwalker]

Looks good overall! Can you write a test to show that a collection created with db.createCollection does inherit the db's readConcern?

Also, I think this commit should be fix(createCollection) instead of perf(readConcern)!

[kvwalker]

Okay so we're seeing the test failures because of the error The field 'readConcern' is not a valid collection option, which makes sense because readConcern is not listed in the options for createCollection in the docs. We can get around this by modifying create_collection.js's illegalCommandFields to include readConcern.

[kvwalker]

looks good to me! 🎉